1. FIELD OF THE INVENTION
This invention relates to a photosensitive, pressure-sensitive recording sheet of plain paper transfer type.
2. PRIOR ART
Conventionally known pressure-sensitive copying papers consist of (a) an upper sheet formed by dissolving a colorless, electron-donating color former in a non-volatile oil or the like, encapsulating the resulting color former-containing oil as a core substance and coating the resulting microcapsules on one side of a substrate and (b) a lower sheet formed by coating a colorless, electron-accepting color developer on one side of a substrate. An image appears on the lower sheet when the two sheets are superimposed so that their coated sides face each other and printing is applied from the non-coated side (the up side) of the upper sheet with a pen, a typewriter or the like. Also, there are such pressure-sensitive copying papers which use, in place of the color former and the color developer both mentioned above, a metal compound and a ligand to form a chelate for color development. In actual usage of these pressure-sensitive copying papers, there is an incovenience that the upper sheet and the lower sheet must always be used in combination.
There are also pressure-sensitive copying papers of self-contained (self color development) type formed by coating on one side of a substrate both of a color-forming component and a color-developing component. When printing is applied to these papers, an image appears only on the coated side of the substrate. As well known, when a self-contained pressure-sensitive copying paper and a plain paper are superimposed so that the plain paper faces the coated side of the copying paper and printing is applied, an image appears only on the coated paper and there occurs no transfer of the image onto the plain paper.
The term "plain paper" used in the specification means a substrate containing neither reactant (e.g. electron-donating color former) nor coreactant (e.g. electron-accepting color developer), or a coated paper formed by coating a plain paper with a metal compound and/or an inorganic pigment.
Pressure-sensitive copying papers consisting of a substrate coated on one side with a color former (a reactant or a coreactant) and a color developer (a coreactant or a reactant) and capable of forming a transferred image on a plain paper are disclosed in Japanese Patent Application Kokai (Laid-open) No. 126111/1979 and Japanese Patent Publication No. 16728/1978.
Japanese Patent Application Kokai (Laid-open) No. 126111/1979 discloses that a coating color comprising a solid color former, a solid color developer and a wax is coated on a substrate in a single layer and that the coating color develops a color at the moment when the color former and the color developer are mixed. Hence, the above literature relates to a pressure-sensitive transfer material having a colored coating layer like a back carbon paper. Because of its colored coating layer, this material is disadvantageous in appearance.
Japanese Patent Publication No. 16728/1978 relates to color development by chelate. Microcapsules containing a reactant are coated on a substrate and then a solution of a coreactant in colvent is coated thereon. Since a solvent is used, the wall materials of said microcapsules must be resistant to the solvent and accordingly are restricted. This color development is disadvantageous also in environmental and economical aspects.
Pressure-sensitive copying papers having improved transferability onto a plain paper are disclosed in Japanese Patent Application Kokai (Laid-open) Nos. 121790/1981 and 207088/1982.
Japanese Patent Application Kokai (Laid-open) No. 121790/1981 discloses a plain paper transfer type pressure-sensitive copying paper obtained by coating on one side of a substrate a mixture comprising an electron-donating color former, an electron-accepting color developer and a wax. This paper is characterized by using, as the wax, a combination of two waxes, namely, an amide wax and another wax.
Japanese Patent Application Kokai (Laid-open) No. 207088/1982 discloses a plain paper transfer type pressure-sensitive copying paper obtained by coating on the back side of a substrate a ligand, a metal compound and a wax in a single layer.
These plain paper transfer type pressure-sensitive copying papers have good transferability onto a plain paper. Further, with these papers, also copying is possible as necessary by coating the whole surface or only the required parts of the substrate.
With these pressure-sensitive copying papers, however, transfer onto a plain paper is made only in a single color. That is, only one color-forming component is coated on a substrate to attain the object. Even if a plurality of color-forming components are coated, only a one mixed color is transferred.